A. Field of the Invention
This invention relates in general to machines for turning and milling workpieces, and more particularly, turning machine chucks and methods of positioning workpieces in turning machines.
B. Description of the Prior Art
The history of turning, milling and tapping machines and the art of operating these machines is extensive. As labor costs have increased, it has become increasingly important to reduce the time for changing bits and rechucking workpieces in these machines. These processes are labor intensive. At the same time, consistency and accurate control of the milling, turning and tapping are required. Achieving the goals of reducing operation time while increasing accuracy is a difficult task and much design work has been devoted to it.
One of the most difficult problems in the design and operation of turning machines involves workpieces which must be turned on more than one axis. Of course, in order to machine on a first axis, the workpiece must be positioned in a chuck with the workpiece aligned on the first axis. Since the relation between the first and second axis of turning is usually critical, the first and second positioning operations must be very carefully made. As a workpiece is fixed in the chuck, the workpiece must be carefully aligned and positioned against locator surfaces in the chuck. This is a time consuming operation. Following machining on the first axis, this time consuming manual operation must be performed on the second axis. Thus, a critical second aligning operation must be done by hand and the hand alignment is both slow and less accurate. Further, it is often not easy to provide a single chuck with locator surfaces capable of grasping and precisely aligning the workpiece for both axes. Thus, some dual axis workpieces require two different turning machines or at least two chucks in addition to two manual chuck loading operations.
One attempt to solve this problem involves a rotatable chuck jaw. A workpiece is clamped in position in the chuck jaw and the chuck jaw is then wedged in a first position for turning along a first turning axis of the workpiece. Following the first turning axis operations the chuck rotation is stopped and the chuck jaw is unclamped from the chuck body. The chuck jaw is hingedly connected to the chuck body so that after unclamping it can be manually rotated to a second turning axis position. The jaw is then clamped again. Clamping of the jaw is achieved by a wedge being fixed against flat positioning surfaces on a periphery of the jaw adjacent the hinge between the jaw and chuck body.
Although the rotatable jaw has advantages over manually rechucking the workpiece, it is not possible to use such a rotating jaw when the second turning axis is not merely rotationally related to the first. For example, if the second turning axis requires that the workpiece be rotated and translated (moved up or down with respect to the axis of the jaw rotation, for example), a rotation of the jaw cannot correctly reposition the workpiece. Further, the rotating chuck still requires manual rotation of the chuck and this means the turning machine must be completely stopped, the machine opened, the jaw unclamped, manually rotated, reclamped, the machine closed, and then reactivated. This is still a time consuming and labor intensive process. This machine and process, therefore, still have not overcome the problem.